KR101501334B1 - Method for Estimating Frequency Offset based on OFDM System and Apparatus Thereof - Google Patents

Abstract

The present invention relates to a method and an apparatus for estimating a frequency error based on an OFDM system. A frequency error estimation method based on an OFDM system according to the present invention includes the steps of receiving an OFDM signal in which a pilot subcarrier is inserted from a transmitter and performing Fourier transform on the received OFDM signal, Grouping the pilot subcarriers having a phase difference into a subset, transforming the pilot subcarriers included in the subset into the same phase, calculating a correlation value between adjacent subcarriers for each subset, And selecting an integer frequency error estimation value at which the sum of the correlation values becomes maximum.
According to the present invention, it is possible to reduce a complex multiplication operation between adjacent subcarriers during a correlation operation between subcarriers, so that computational complexity can be reduced and high accuracy can be maintained compared with the prior art. In addition, it has an effect of reducing the high cost incurred in actual implementation and the number of used hardware.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a frequency offset estimation method based on an OFDM system,

The present invention relates to a frequency error estimation method and apparatus based on an OFDM system, and more particularly, to a frequency error estimation method based on an OFDM system with reduced calculation complexity and high accuracy, ≪ / RTI >

In many wireless broadcasting systems including DRM + system, OFDM method is used in which the entire channel is divided into a plurality of orthogonal subchannels and transmitted in parallel for high-speed data transmission. The OFDM system is robust against multipath fading, has high frequency efficiency, and is advantageous for high-speed communication. However, since OFDM systems are required to maintain the orthogonality between subcarriers because carriers are overlapped to transmit signals when transmitting signals, the OFDM system has a disadvantage that it is very sensitive to frequency errors.

The frequency error is caused by the Doppler effect or the instability of the transmitter / receiver oscillator. The frequency error generated is divided into integer frequency error and fractional frequency error. Due to an integer frequency error occurring in the receiving end, after the Fast Fourier Transform process, the position of the subcarriers is circulated by an integer frequency error, and data demodulation is not normally performed at a desired position.

An integer frequency error estimation method applicable to a DRM + system using only one pilot symbol among methods for estimating a frequency error has been proposed. In the differential detection technique, which is one of the prior art techniques, high computational complexity is required, Cost and high complexity of hardware.

According to the conventional differential detection method, as shown in Equation (1), a point at which a cross-correlation value between adjacent subcarriers of a pilot signal known at a receiving end is multiplied by a cross-correlation value between adjacent subcarriers of a received signal, .

과

이며, P는 파일럿에 포함되는 부반송파 위치를 나타내는 인덱스의 집합, P(k)는 수신단에서 알고 있는 파일럿 심볼, d는 정수배 주파수 오차 추정 시행 값, M은 시스템에서 발진기와 도플러 천이에 의해 발생 할 수 있는 최대 정수배 주파수 오차 범위이며,

는 켤레 복소수를 나타낸다. 두 개의 연속적인 상관 값 표본 사이에 차동 결합된

은 위상이 일정해지며, 구성 요소들의 합에 의해 큰 상관 값을 구할 수 있다.

의 각각의 구성 요소는 실수와 허수 부분으로 나누어지며, 나누어진 부분들을 결합시키기 위해

의 포락선을 구하는 방식으로 이루어진다. From here

and

Where P is a set of indices indicating the positions of subcarriers included in the pilot, P (k) is a known pilot symbol, d is an integer frequency error estimation execution value, and M is an oscillator and Doppler shift in the system The maximum integer frequency error range,

Represents a complex conjugate. Differentially coupled between two consecutive correlation value samples

The phase is constant, and a large correlation value can be obtained by the sum of the components.

Each component of the function is divided into a real number and an imaginary part,

Is obtained by the method of finding the envelope of.

The differential detection technique according to the related art can estimate the integer frequency error, but has a problem of having high computational complexity because the correlation value between consecutive pilot subcarriers must be further calculated.

The technology which is the background of the present invention is disclosed in Korean Patent Registration No. 10-1063072 (published on Mar. 19, 2011).

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method and an apparatus for estimating a frequency error based on an OFDM system that reduces computational complexity and maintains high accuracy in an integer frequency error estimation.

A frequency error estimation method based on an OFDM system according to an embodiment of the present invention includes: receiving an OFDM signal in which a pilot subcarrier is inserted from a transmitter; performing a Fourier transform on the received OFDM signal; The method includes the steps of: grouping pilot subcarriers having a specific phase difference among pilot subcarriers having a specific phase difference among pilot subcarriers having a specific phase difference, converting pilot subcarriers included in the subset into the same phase, calculating a correlation value between adjacent subcarriers, Summing the correlation values obtained from the respective subsets, and selecting an integer frequency error estimation value at which the sum of the correlation values becomes maximum.

And storing the inserted position and phase of the pilot subcarrier.

The step of receiving and performing the Fourier transform on the OFDM signal may generate the following subcarrier signal Y (k) through the Fourier transform.

는 부반송파 간격으로 정규화된 정수배 주파수 오차, Y(k)는 주파수 영역의 수신된 OFDM 신호의 k번째 부반송파 신호,

은

의

만큼 순환 이동된 송신 심볼이고, H(k)는 주파수영역의 채널 응답이며, W(k)는 백색 가우시안 잡음(AWGN)이다.From here

Y (k) is the k-th subcarrier signal of the received OFDM signal in the frequency domain,

silver

of

(K) is the channel response of the frequency domain, and W (k) is the white Gaussian noise (AWGN).

The pilot subcarriers can be expressed by the following equation.

P (k) denotes a k-th signal of the pilot subcarrier, and θ (k) denotes a predetermined phase value of the pilot subcarrier.

)를 하기 수학식에 적용하여 R(k)를 연산하는 단계, 그리고 상기 R(k)가

값 중 어느 하나인 경우, 해당되는 부반송파 인덱스(k)를 상기 최소 인덱스(

)와 동일한 부그룹에 포함시키는 단계를 포함할 수 있다. The step of grouping the pilot subcarriers as a subset may include: selecting a minimum index among the ungrouped pilot subcarrier indexes

) To the following equation to calculate R (k), and R (k)

Value, the sub-carrier index (k) is stored in the minimum index (

) In the same sub-group as the first sub-group.

중 어느 하나에 해당할 수 있다. The specific phase difference

Or the like.

The step of converting the pilot subcarriers included in the subset into the same phase may be converted to the same phase using R (k) as shown in the following equation.

이다. here,

to be.

The step of summing the correlation values obtained in the respective subsets may be expressed by the following equation.

Here, Z (k + d) is a value obtained by summing up the correlation values of N _s subsets, d is an integer frequency error candidate value, | d || M, and M is an integer frequency error range Variable.

)으로 추정할 수 있다. The step of selecting a frequency error estimation value at which the sum of the correlation values is maximum may be performed by multiplying an integer frequency error candidate value (d) such that the sum of the correlation values becomes a maximum as an integer frequency error value

).

An apparatus for estimating a frequency error based on an OFDM system according to another embodiment of the present invention includes: a receiver for receiving an OFDM signal in which a pilot subcarrier is inserted from a transmitter and for receiving the OFDM signal; a Fourier transformer; a pilot subcarrier A pilot subset selecting unit for grouping pilot subcarriers having a specific phase difference among subcarriers into a subset, a phase shifter for converting the pilot subcarriers included in the subset into the same phase, A correlation processor for calculating a correlation value and summing the correlation values obtained in each subset and a frequency error estimator for selecting an integer frequency error estimation value at which the sum of the correlation values becomes maximum.

As described above, according to the present invention, it is possible to reduce the complex multiplication operation between adjacent subcarriers during the correlation operation between subcarriers, so that computational complexity can be reduced and high accuracy can be maintained compared with the prior art. In addition, it has an effect of reducing the high cost incurred in actual implementation and the number of used hardware.

1 is a diagram illustrating a configuration of a frequency error estimation apparatus based on OFDM according to an embodiment of the present invention.
FIG. 2 is a flowchart for explaining an integer frequency error estimation method of the frequency error estimation apparatus according to FIG.
FIG. 3 is a diagram for explaining how the pilot subset selector according to the embodiment of the present invention is divided into subsets for pilot subcarriers.
FIG. 4 is a graph illustrating the frequency error estimation performance of an integer frequency error estimation apparatus according to an embodiment of the present invention.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the present invention.

Hereinafter, an integer-frequency error estimation apparatus 100 in an OFDM-based DRM + system to which an integer-frequency error estimation method according to the present invention is applied will be described in detail with reference to the accompanying drawings.

1 is a diagram illustrating a configuration of a frequency error estimation apparatus based on OFDM according to an embodiment of the present invention.

1, a frequency offset estimation apparatus 100 according to an exemplary embodiment of the present invention corresponds to a receiver for receiving an OFDM signal and includes a Fourier transform unit 110, a pilot information storage unit 120, a pilot subset selection unit 130, a phase shifting unit 140, a correlation processing unit 150, and a frequency error estimating unit 160.

First, the fast Fourier transform unit 110 receives an OFDM signal with a pilot subcarrier inserted therein, and performs signal processing on the received OFDM signal by FFT-transforming the received OFDM signal on the frequency axis. The pilot information storage unit 120 stores total pilot information, and the pilot information includes a predetermined insertion position and phase of pilot subcarriers.

The pilot subset selector 130 divides the total pilot subcarriers into subsets each consisting of pilot subcarriers having a specific phase difference. Then, the phase converter 140 rotates the phases of the pilot subcarriers included in each subset equally.

The correlation processing unit 150 calculates a correlation value between adjacent subcarriers for each subset, and sums the correlation values obtained in each subset. The frequency error estimation unit 160 selects the largest correlation value among the values calculated through the correlation processing unit 150 and selects the final integer frequency error value.

FIG. 2 is a flowchart for explaining an integer frequency error estimation method of the frequency error estimation apparatus according to FIG.

First, according to an embodiment of the present invention, a transmitter transmits an OFDM-based DRM + system transmission signal having N subcarriers to an Inverse Fast Fourier Transform (IFFT) and then transmits the DRM + system transmission signal to a frequency error estimation apparatus 100. Here, a TRC pilot existing only in the first OFDM symbol of each transmission frame is transmitted once every 5 ms, and the TRC pilot is used for frame synchronization and frequency synchronization. The pilot subcarriers are inserted in setting positions known to the transmitting end and the receiving end (frequency error estimating device 100) respectively.

The transmission signal after the inverse fast Fourier transform (IFFT) of the symbols generated in the transmitter is expressed by Equation (2).

Here, each OFDM symbol uses N subcarriers, and X (k) is data modulated by the M-PSK modulation technique.

The transmitted OFDM symbol X (k) is composed of N _trc pilot subcarriers and NN _trc subcarriers of information data.

 Here, D and P are sets of indices indicating subcarrier positions in which information data and pilot are included, respectively. The pilot subcarrier P (k) can be expressed by the following Equation (4).

의 계수를 가지며, DRM+ 시스템에서 파일럿 부반송파의 개수는 N_trc=21로 설정된다. (K) denotes a predetermined phase value of pilot subcarriers, and P (k) denotes a pre-

, And the number of pilot subcarriers in the DRM + system is set to N _trc = 21.

2, the Fourier transform unit 110 receives an OFDM signal in which a pilot subcarrier is inserted from a transmitter and performs Fast Fourier Transform (FFT) on the frequency axis on the time axis of the received OFDM signal (S210)

In this case, in the OFDM system, the time synchronization error and the decimal multiplication error cause the inter-symbol interference (ICI) after the fast Fourier transform process (S210). Therefore, . Assuming that a fractional frequency error and a time synchronization error are compensated, the OFDM symbol in the frequency axis is expressed by Equation (5).

는 부반송파 간격으로 정규화된 정수배 주파수 오차, Y(k)는 주파수 영역의 수신된 OFDM 신호의 k번째 부반송파 신호,

은

의

만큼 순환 이동된 심볼이고, H(k)는 주파수영역의 채널 응답이며, W(k)는 백색 가우시안 잡음(AWGN)이다. From here

Y (k) is the k-th subcarrier signal of the received OFDM signal in the frequency domain,

silver

of

(K) is the frequency response in the frequency domain, and W (k) is the white Gaussian noise (AWGN).

The pilot subset selector 130 groups the pilot subcarriers of the signal converted to the frequency axis into a subset of pilot subcarriers having a specific phase difference (S220).

를 가지는 파일럿 부반송파들로 구성된 여러 개의 부집합으로 나누고, 각 부집합별로 차동 검출 기법을 적용하여 정수배 주파수 오차를 추정한다. That is, in order to reduce the amount of computation of the differential detection technique according to the related art, the pilot subset selector 130 according to the embodiment of the present invention calculates the phase difference between adjacent pilot subcarriers with respect to the entire pilot subcarrier set

, And estimates the integer frequency error by applying a differential detection technique to each subset.

FIG. 3 is a diagram for explaining how the pilot subset selector according to the embodiment of the present invention is divided into subsets for pilot subcarriers.

이고, 파일럿의 부반송파 인덱스(k)가 -80인 경우, 위상 인덱스(P(-80))는 수학식 4에 의하여

이다. As shown in FIG. 3, a phase index value for a subcarrier index k of 21 pilots is stored in the pilot information storage unit 120. In FIG. For example, when the subcarrier index k of the pilot is -81, the phase index P (-81)

And the sub-carrier index k of the pilot is -80, the phase index P (-80)

to be.

Then, pilot subset selector 130 calculates R (k) for subcarrier indices (k) of the pilot as shown in Equation (6) below.

는 TRC 파일럿의 부반송파 인덱스(k)들 중에서 최소 인덱스를 나타내며, 도 3과 같은 예에서는 -81이 된다. here,

Represents the minimum index among the subcarrier indexes (k) of the TRC pilot, and is -81 in the example shown in FIG.

(-80), R (-79), and R (-53) are obtained by using Equation (6).

값에 포함되는 반면, R(-53)은 복소수 형태인 -0.4660+0.8848j 로서

값에 포함되지 않는다. As a result of the calculation, R (-80) is -j and R (-79) is -1, as shown in Equation (7)

Value, while R (-53) is in the complex form of -0.4660 + 0.8848j

It is not included in the value.

값에 포함된다는 것은 파일럿 부반송파간의 위상 차이가

에 포함된다는 것을 의미하므로, 파일럿 부집합 선택부(130)는 R(k)을 통하여 파일럿 부반송파간의 위상 차이가

중 어느 하나에 해당하는 파일럿 부반송파를 하나의 부그룹으로 선택하게 되는 것이다. That is, if the value of R (k)

Included in the value is that the phase difference between the pilot subcarriers is

, The pilot subset selector 130 determines that the phase difference between the pilot subcarriers is R (k)

The pilot subcarriers corresponding to one of the pilot subcarriers are selected as one subgroup.

In this manner, the pilot subset selector 130 forms the first subset when the pilot subcarrier index k is -81, -80 and -79. When the subcarrier index k is -53, the pilot subset selector 130 selects -81 , -80, and -79, respectively.

)로 설정된다. As described above, when the sub-carrier index k of the pilot is -81, -80, and -79, if the grouping is performed as one sub-set, the minimum index -53 of the remaining 18 indexes k that are not grouped is minimized index(

).

R (-52), R (-51), and R (-32) are obtained using Equation (6) as in Equation (7).

값에 포함되는 반면, R(-32)는 복소수 형태인 -0.5194+0.8546j 로서

값에 포함되지 않는다. As a result of the calculation, R (-52) is 1 and R (-51) is -1, as shown in Equation (8)

Value, while R (-32) is in the complex form -0.5194 + 0.8546j

It is not included in the value.

Accordingly, the pilot subset selector 130 forms a second subset when the subcarrier index k of the pilot is -53, -52, -51, -53 when the subcarrier index k is -32, -52, and -51, respectively.

으로 설정된다. When the sub-carrier indexes (k) of the pilot are -53, -52, and -51, if the grouping is performed as one subset, the minimum index -32 of the remaining 15 indexes (k)

.

In this way, the pilot subset selector 130 groups the subcarrier indices (k) of the remaining 15 pilots into subsets. As a result, the pilot subset selector 130 is grouped into eight subsets as shown in FIG.

와 같이 나타낼 수 있다. 그리고, N_s=8개의 부집합으로 나누어지며, P={{-81,-80-79}, {-53,-52,-51}, {-32,-31}, {12,13,14}, {21,22,23}, {40,41,42}, {67,68}, {80,81}}과 같이 나눌 수 있다. That is, as shown in FIG. 3, the set P of indexes of all pilot subcarriers is

As shown in Fig. And, N _s = is divided into eight sub-set, P = {{- 81, -80-79}, {-53, -52, -51}, {-32, -31}, {12,13, 14}, {21,22,23}, {40,41,42}, {67,68}, {80,81}}.

에 대하여 다음의 수학식 9와 같이 나타낼 수 있다. The operation of the pilot subset selector 130 is summarized as follows. The minimum index among the subcarrier indexes (k) of the TRC pilot

Can be expressed by the following equation (9).

는 P_s 중 가장 작은 부반송파 인덱스, 전체 파일럿 인덱스 집합 P는

이며, P_n은 선택될 n번째 파일럿 부집합에 존재하는 파일럿 부반송파 인덱스 집합, r_n은 P의 부반송파 인덱스를 나타내며,

은 n번째 파일럿 부집합 P_n의 첫번째 부반송파를 의미한다. 이 때, n번째 파일럿 부집합 P_n은 상기 수학식 6을 만족할 때 생성된다.here

Is the smallest subcarrier index among P _s , and the total pilot index set P is

P _n denotes a pilot subcarrier index set in the n-th pilot subset to be selected, r _n denotes a subcarrier index of P,

_Denotes the first subcarrier of the n-th pilot subset P _n . At this time, the n-th pilot subsets P _n are generated when the above Equation (6) is satisfied.

값을 가지는 파일럿 부반송파들을 하나의 부집합으로 그룹핑한다. In this way, the pilot subset selector 130 can calculate the pilot sub-carrier selection result (R (k)) between the pilot subcarriers by Equation (6)

≪ / RTI > are grouped into one subset.

In addition, the phase shifter 140 transforms the pilot subcarriers in each subset into the same phase in order to reduce the computational complexity (S230). That is, the phase converter 140 multiplies the values of R (k) by Equation (10) to convert the phases of the pilots belonging to the same subset equally.

이며,

는 통계적으로

와 거의 유사하다.

는

중 하나의 값으로

(

)가 n 번째 부집합의 첫 번째 파일럿 부반송파

의 위상과 동일한 위상을 갖도록 선택되는 것이다. here

Lt;

Statistically

.

The

With one of the values

(

) Is the first pilot subcarrier of the n < th >

The phase of the signal is selected to have the same phase as the phase of the signal.

의 위상과 동일하게 만들어줌으로써, P_n 을 결정하는 동위상 변환 파라미터로 작용한다. Thus, R (k) obtained from Equation (6) is the phase of the pilot subcarrier P (k) as the first subcarrier of each subset

So that P _n Lt; RTI ID = 0.0 > a < / RTI >

Next, the correlation processing unit 150 calculates the correlation value between adjacent subcarriers for each subset, and adds the correlation values obtained in each subset (S240). That is, as shown in Equation (11), the correlation processing unit 150 calculates a correlation value between adjacent subcarriers in a subset, and adds the correlation values obtained in each subset.

Here, Z (k + d) is a summation value of N _s subsets of correlation values, and d is an integer frequency error candidate value, corresponding to | d || M. Here, M is a variable indicating an integer frequency error range that can be generated at the receiving end (the frequency error estimating apparatus 100). For example, when M = 2, the integer frequency error candidate value (d) can be represented by five candidate values of -2, -1, 0, 1,

Next, the frequency error estimation unit 160 selects an integer frequency error candidate value d having the largest correlation sum value among the values calculated through the correlation processing unit 150, and estimates it as a final integer frequency error value ( S250).

)은 다음의 수학식 12와 같이 나타낼 수 있다. In other words, the estimated range of the frequency error of the whole integer to be finally obtained is determined as the estimated value by comparing the correlation sum of 2M + 1 candidate groups. The estimated integer frequency error value

) Can be expressed by the following Equation (12).

Therefore, if the integer frequency error candidate value d is five candidate values of -2, -1, 0, 1, and 2, the five values are substituted into d, and then the largest correlation sum value is obtained d value, and estimates the selected d value as the final integer frequency error value.

As described above, according to the embodiment of the present invention, all pilot subcarriers of the received signal are modulated to have the same phase for each subset using the calculated R (k) value after dividing the entire pilot symbol into 8 subsets. Then, correlation values between adjacent pilot subcarriers in each subset are obtained, and the resultant values are added to select a final estimation value. Table 1 is a table for comparing the integer complex frequency error estimation method according to the embodiment of the present invention and the computational complexity of the prior art.

Estimation method Complex addition operations Number of Complex Multiplication Operations Differential detection technique

The estimation method according to the embodiment of the present invention

When expressing the computational complexity of the estimator integer frequency error according to an embodiment of the present invention as shown in Table 1 to a complex number multiplication number N _S However, the conventional method requires a complex multiplication operation of N _trc -1. Assuming that the two real addition operations are the same as one complex addition operation, the number of complex addition operations according to the embodiment of the present invention requires N _s -1 complex addition operation. However, the conventional method requires N _trc - Two complex addition operations are required.

That is, as shown in Equations (11) and (12), according to the embodiment of the present invention, the complex multiplication is performed on the adjacent pilot subcarriers belonging to each subset, and the multiplication result for each subset is added. _S complex multiplication operation and N _S -1 complex addition operation are required.

In contrast, according to the conventional technique, since the grouping operation is not performed to the N _S subgroups, the multiplication and addition operations must be performed on all the adjacent pilot subcarriers as shown in Equation (1), so that N _trc -1 complex multiplication operations and N _trc A complex addition operation of -2 is required.

Compared to the conventional method, the method according to the embodiment of the present invention reduces the number of operations of the complex multiplication by 40.0% and the complex addition operation by 36.8% .

Hereinafter, a frequency error estimation performance of an integer frequency error estimation apparatus according to an embodiment of the present invention will be described with reference to FIG.

FIG. 4 is a graph illustrating the frequency error estimation performance of an integer frequency error estimation apparatus according to an embodiment of the present invention.

For practical implementation of the integer frequency error estimation apparatus according to the embodiment of the present invention, the present invention is applied to an OFDM system with a bandwidth of 100 KHz, with N = 213, N _g = 21, and N _trc = 21 conforming to the DRM + . The OFDM system uses five channel models (Urban (Slow), Urban (Fast), CM2, Rural (CM3), Terrain obstructed (CM4) and Hilly terrain Respectively. Urban (slow), Urban (Fast), Rural and Terrain obstructed channels are EIA channel models used for performance analysis of broadcasting systems. Hilly terrain channels are DAB hilly terrain channel models with relatively long ehco components.

FIG. 4 is a graph illustrating an integer frequency error estimation failure probability when the conventional method according to the SNR and the method according to an embodiment of the present invention are used in the five channel model environment. As shown in FIG. 4, in a flat channel environment such as Urban (CM1), Urban (Fast) (CM2), and Rural (CM3) channels, performance difference occurs due to the Doppler effect depending on the channel movement speed. It can be confirmed that the frequency estimation failure probability is similar to the present invention (Proposed).

Also, in the case of Terrain obstructed (CM4) and Hilly terrain (CM5) channels, the frequency selective characteristic becomes larger due to the increase of the maximum delay of the channel. As a result, both the conventional method and the proposed method show a decrease in the integer frequency error estimation performance, but it is confirmed that the conventional method and the estimation performance of the proposed method have similar performance.

As shown in FIG. 4, according to the embodiment of the present invention, it can be seen that the computational complexity is lower than that of the prior art, while the integer frequency error estimation performance is maintained.

As described above, according to the embodiment of the present invention, it is possible to reduce the complex multiplication operation between adjacent subcarriers during the correlation operation between subcarriers, so that computational complexity can be reduced and high accuracy can be maintained compared with the prior art. In addition, it has an effect of reducing the high cost incurred in actual implementation and the number of used hardware.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. Accordingly, the true scope of the present invention should be determined by the technical idea of the appended claims.

100: Frequency error estimation apparatus, 110: Fourier transform unit,
120: pilot information storage unit, 130: pilot subset selection unit,
140: phase conversion unit, 150: correlation processing unit,
160: Frequency error estimating unit

Claims (18)

Receiving an OFDM signal in which a pilot subcarrier is inserted from a transmitting end and performing Fourier transform on the received OFDM signal,
Grouping the pilot subcarriers having a specific phase difference among the pilot subcarriers included in the OFDM signal as a subset,
Converting pilot subcarriers included in the subset to the same phase for each subset,
Calculating correlation values between adjacent subcarriers for each of the subset for each of the integer frequency error candidate values, and summing the correlation values obtained in each subset; and
And selecting the integer frequency error candidate value as the integer frequency error error estimate value such that the sum of the correlation values is maximized,
The grouping of the pilot subcarriers as a subset includes:
Among the pilot subcarrier indices that are not grouped, the minimum index (

) To the following equation to calculate R (k), and
If R (k) is

Value, the sub-carrier index (k) is stored in the minimum index (

) In the same sub-group as the OFDM system.

The method according to claim 1,
And storing an insertion position and a phase of the pilot subcarriers. The method of claim 2,
The receiving and Fourier transforming the OFDM signal includes:
A frequency error estimation method based on an OFDM system that generates the following subcarrier signal Y (k) through the Fourier transform:

From here

Y (k) is the k-th subcarrier signal of the received OFDM signal in the frequency domain,

silver

of

(K) is the channel response of the frequency domain, and W (k) is the white Gaussian noise (AWGN). The method of claim 3,
Wherein the pilot subcarriers are expressed by the following equation:

P (k) denotes a k-th signal of the pilot subcarrier, and θ (k) denotes a predetermined phase value of the pilot subcarrier. delete The method of claim 4,
The specific phase difference

A frequency error estimation method based on an OFDM system corresponding to one of the OFDM systems. The method of claim 4,
The step of transforming the pilot subcarriers included in the subset into the same phase includes:
A frequency error estimation method based on an OFDM system in which R (k) is transformed into the same phase as in the following equation:

here,

to be. The method of claim 7,
Wherein the step of summing the correlation values obtained in each subset comprises:
A frequency error estimation method based on an OFDM system represented by the following equation:

Here, Z (k + d) is a value obtained by summing up the correlation values of N _s subsets, d is an integer frequency error candidate value, | d || M, and M is an integer frequency error range Variable. The method of claim 8,
Selecting the integer frequency error candidate value as the integer frequency error estimation value to maximize the sum of the correlation values,
An integer frequency error candidate value d for making the sum of the correlation values become a maximum is defined as an integer frequency error value d

) Based on an OFDM system.

Receiving an OFDM signal in which a pilot subcarrier is inserted from a transmitting end, and transmitting the received OFDM signal to a Fourier transformer,
A pilot subset selection unit for grouping subset of pilot subcarriers having a specific phase difference among pilot subcarriers included in the OFDM signal,
A phase converter for converting the pilot subcarriers included in the subset to the same phase for each subset,
A correlation processor for calculating a correlation value between adjacent subcarriers for each of the subset for each of the integer frequency error candidate values and summing the correlation values obtained in each subset,
And a frequency error estimator for selecting an integer frequency error candidate value as an integer frequency error error estimate value so that the sum of the correlation values becomes a maximum,
Wherein the pilot sub-
Among the pilot subcarrier indices that are not grouped, the minimum index (

) Is applied to the following equation to calculate R (k)
If R (k) is

Value, the sub-carrier index (k) is stored in the minimum index (

) In the same sub-group as the OFDM system.

The method of claim 10,
And a pilot information storage unit for storing an inserted position and phase of the pilot subcarriers. The method of claim 11,
Wherein the Fourier transform unit comprises:
A frequency error estimator based on an OFDM system for generating the following subcarrier signal Y (k) through the Fourier transform:

From here

Y (k) is the k-th subcarrier signal of the received OFDM signal in the frequency domain,

silver

of

(K) is the channel response of the frequency domain, and W (k) is the white Gaussian noise (AWGN). The method of claim 12,
Wherein the pilot subcarriers are expressed by the following equation:

P (k) denotes a k-th signal of the pilot subcarrier, and θ (k) denotes a predetermined phase value of the pilot subcarrier. delete 14. The method of claim 13,
The specific phase difference

A frequency error estimator based on the OFDM system. 14. The method of claim 13,
The phase-
A frequency error estimation apparatus based on an OFDM system in which R (k) is transformed into the same phase as in the following equation:

here,

to be. 18. The method of claim 16,
Wherein the correlation processing unit
A frequency error estimation apparatus based on an OFDM system represented by the following equation:

Here, Z (k + d) is a value obtained by summing up the correlation values of N _s subsets, d is an integer frequency error candidate value, | d || M, and M is an integer frequency error range Variable. 18. The method of claim 17,
The frequency-
An integer frequency error candidate value d for making the sum of the correlation values become a maximum is defined as an integer frequency error value d

) Based on an OFDM system.

Images